Babies are born with about 300 bones, but adults have only 206.
Why it is true
Babies are born with about 300 bones, many of which are cartilage. During growth, some bones fuse together. That is why an adult has only 206 bones. The fusion process continues until about 25 years of age.
Source: Anatomy
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.